A thermal recording system for obtaining recorded images simultaneously with the application of input signals is widely used in facsimile machines, computer terminal printers, and printers for measuring equipment because the apparatus used in a thermal recording system is relatively simple and inexpensive, and it is of low noise.
The recording medium most commonly used in such a thermal recording system is a so-called color formation-type heat-sensitive recording paper, which is provided with a recording layer which undergoes physical and chemical changes on heating to cause color formation. This recording medium, however, has several disadvantages. One of the disadvantages is that the recording medium is liable to cause unnecessary color formation during the production or storage thereof. Another disadvantage is that the storage stability of images recorded on this medium is poor. For example, images so produced exhibit a fading phenomenon when brought into contact with organic solvents or chemicals.
In order to overcome the above problems, a recording system has been proposed in which a recording medium utilizing a coloring material which is colored itself is used in place of the above color formation-type heat-sensitive recording paper. For example, Japanese Patent Application (OPI) No. 15446/76 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") discloses a recording system in which a substrate, such as paper and a polymer film, coated with a coloring material which is solid or semi-solid at room temperature is superposed on a recording paper (image-receiving paper) in such a manner that the coloring material coated on the substrate comes into contact with the recording paper. Then the coloring material is selectively transferred to the recording paper by heating the substrate with a thermal recording head, thereby recording a desired image.
In this recording system, the coloring material on the substrate is melted, evaporated, and sublimated by the application of heat. Then it is transferred to the recording paper and fixed thereon by the action of sticking, adsorption, and dye-fixing, to thereby form a recorded image. One of the characteristic features of this recording system is that plain paper (non-coated paper) can be used as the recording paper. However, when plain paper is used as the recording paper, the dye-fixing, in particular, is difficult to accomplish. As a result, not only is the resulting recorded image low in color density, but a serious fading phenomenon also occurs over a lapse of time.